LoongArch: Fix earlycon parameter if KASAN enabled

LoongArch: Fix earlycon parameter if KASAN enabled

commit 639420e9f6cd9ca074732b17ac450d2518d5937f upstream.

The earlycon parameter is based on fixmap, and fixmap addresses are not
supposed to be shadowed by KASAN. So return the kasan_early_shadow_page
in kasan_mem_to_shadow() if the input address is above FIXADDR_START.
Otherwise earlycon cannot work after kasan_init().

Cc: stable@vger.kernel.org
Fixes: 5aa4ac64e6add3e ("LoongArch: Add KASAN (Kernel Address Sanitizer) support")
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>